What is HSRP and VRRP?
Why Interviewers Ask This
This tests whether you can apply Networking knowledge to real-world scenarios. Interviewers are looking for clarity of thought and evidence that you've encountered this in production code.
Answer
HSRP (Hot Standby Router Protocol) and VRRP (Virtual Router Redundancy Protocol) are First-Hop Redundancy Protocols (FHRPs) that provide a virtual default gateway IP address shared between multiple physical routers. If the active router fails, the standby router takes over within seconds, maintaining connectivity. HSRP is Cisco-proprietary. An active router and standby router share a virtual IP and virtual MAC address. Hosts use the virtual IP as their default gateway. If the active router fails, the standby becomes active after a hold timer expires. VRRP (RFC 5798) is the open standard equivalent — one master and multiple backup routers share a virtual IP. GLBP (Gateway Load Balancing Protocol) is Cisco's improvement that load-balances across multiple routers rather than having one idle standby. All three provide sub-second failover with proper tuning, making the gateway transparent to end users.
Pro Tip
If you're unsure about a detail, say so honestly and explain your reasoning. Interviewers respect candidates who can think through uncertainty rather than bluffing.